Move block loops into sparse.c with iterator helpers in backed_block.c.
Simplify chunk writing by moving skip chunk calls from output_file.c to
sparse.c.
Rename variables to be consistent with new naming.
Remove use of u8, u32, u64.
Change-Id: Ic138ad58bef9f96239266ccee12ee83ea285e7eb
This moves an exact copy of libsparse from
system/extras/ext4_utils/libsparse to system/core/libsparse in
preparation for linking tools in system/core against it.
Change-Id: If664e4fcfd6612844ac745589beb1517e7f9fe58
